Characterization of Raman Scattering in Solid Samples with Different Particle Sizes and Elucidation on the Trends of Particle Size-Dependent Intensity Variations in Relation to Changes in the Sizes of Laser Illumination and Detection Area

Portable Raman spectroscopy coupled with PLSR analysis for monitoring and predicting of the quality of fresh-cut Chinese yam at different storage temperatures

Portable Raman spectroscopy coupled with partial least squares regression (PLSR) model was performed for monitoring and predicting four quality indicators, moisture content, water activity, polysaccharide content and microbial content of the fresh-cut Chinese yam at different storage temperatures. The variations in the four key indicators were first depicted through a spider web diagram as the storage temperature changed. More importantly, the four key indicators can be accurately monitored and predicted through optimized PLSR models combining with Raman spectroscopy. Among all of the PLSR models for the four indicators, the regression model for moisture content was relatively the best. In addition, storage temperature played a significant role on the model performance of PLSR. The model performance for all indicators at room temperature and high temperature was better than the corresponding PLSR models at refrigeration and freezing conditions. Especially at 25 ℃, the R2 in the calibration set basically reached 0.9. These observations indicated that portable Raman spectroscopy, a simple and easy-to-use detection technique, can monitor and predict the multiple quality indicators of fresh-cut Chinese yam combined with effectively PLSR model, which would be conducive to their applications in food industry.

An axially slanted illumination back-scattering Raman scheme for direct determination of component concentration of powder samples housed in a glass container

For direct and non-sampling determination of the component concentration of a sample housed in a glass container, an axially slanted illumination (ASI) back-scattering Raman scheme that reduces glass background interference has been demonstrated. The strategy was to increase the distance between the spots illuminated by the laser on the glass container and the housed sample in back-scattering measurement. For realization, the laser initially illuminated at a slant through the upper side of the vial wall (sample-unoccupied space) and reach the top of the sample. By this way, fewer number of generated glass photons could be recognized by a detector since they are farther from the focal plane (sample-illumination spot). The concentration of rosuvastatin (2.98-4.14 wt%) in rosulord samples (mixed with five other excipients) was determined using the ASI back-scattering measurement. When the angle of illumination to the vertical axis was 30° and the distance from the center of the laser spot on the glass wall to the center of spot on the sample (DG-S) was 14.9 mm, the sample peaks became more apparent and characteristic due to the reduced glass background. The accuracy of the concentration measurement was superior to that obtained through conventional back-scattering, in which the DG-S was nearly zero. The proposed scheme provides a simple optical setting to suppress the glass background and takes advantage of the sensitivity of Raman analysis through back-scattering measurement, indicating it as an attractive option for through-container analysis.

A Comparative Study of Applying Backscattering and Transmission Raman Spectroscopy to Quantify Solid-State Form Conversion in Pharmaceutical Tablets

Selecting appropriate Raman measurement and data processing method are of importance to enable effective quantification of solid form conversions upon processing or storage. Therefore, a comparative evaluation is presented herein on using backscattering and transmission Raman spectroscopy to quantify salt disproportionation in tablet matrices. The second part focuses on different spectra processing approaches and calibration models for quantifications. Finally, samples under different mechanical stresses were comprehensively analyzed using different Raman measurements. Much as transmission Raman spectrometry may provide accuracy on bulk measurements by having large sampling volume, it has the drawback of signal attenuation and may overlook process-induced phase transitions occurring on local regions of tablet surface. To overcome this limitation, backscattering Raman with deliberate subsampling can be used as an orthogonal method to probe the existence of low-level form conversion distributed over a tablet's surface. In the present case, different levels of the form conversions were found at the edge and the center of tablets due to the uneven shear stress distribution invoked during tablet compression. In such a scenario, it would be beneficial to apply deliberate-focused backscattering and transmission Raman spectrometry together as complementary techniques to capture chemical information both locally and within the bulk of the tablet.

Spatially offset Raman scattering line-mapping as a potential tool for particle size analysis

A spatially offset Raman spectroscopy (SORS) line-mapping scheme was explored as a tool for the measurement of particle size. The proposed scheme is based on the fact that photon migration in powder packing varies as a function of the reduced scattering coefficient, which is directly related to the particle size of the sample. It is known that a smaller particle yields a larger reduced scattering coefficient. Therefore, recognition of the particle size-dependent photon migration (distribution) could be a means to determine the sample's particle size and SORS is a versatile tool for this purpose. Peak intensities acquired along the SORS mapping line are expected to decrease with an increase of the offset distance and the descending slope of the peak intensity can be translated into particle size, for example, a greater slope (steeper intensity decrease) for smaller particles yielding a narrower (denser) photon distribution. For the study, low-density polyethylene (LDPE) and middle-density PE (MDPE) powders with four particle sizes were measured. In each case, the slope of intensity decrease became less steep with the increase of particle size due to the broader photon distribution. A comparative analysis of LDPE and MDPE spectra found that the slope was steeper in the measurement of MDPE powder since the photon distribution was narrower owing to the high particle density. Together, these findings suggest that the proposed scheme is potentially expandable to measure particle sizes of samples with relevant prior calibration and provide useful information on sample composition also for chemical analysis.

Influence of interfering co-appearing container peaks on the accuracy of direct quantitative Raman measurement of a sample in a plastic container

The axially perpendicular offset (APO) scheme was previously demonstrated as a versatile scheme able to minimize or eliminate the glass background in the direct and non-sampling Raman measurement of an ethanol sample housed in a glass bottle. Alternatively, when directly analyzing a sample housed in a plastic container, another typical container yielding strong Raman peaks itself, the Raman peaks of both the container and the housed sample are unavoidably present together in a collected spectrum. Therefore, a crucial issue to investigate under this situation is how the magnitude of the co-appearing container peaks influences the accuracy for quantitative analysis of the housed sample. For the evaluation, a non-sampling Raman spectroscopic measurement of the urea concentration in a urea gel housed in a circular polypropylene (PP) container was attempted by employing two axially perpendicular offset (APO) schemes with detection windows of different sizes (25.4 and 10.0 mm, referred to as the wide-window APO (WW-APO) and narrow-window APO (NW-APO), respectively), and transmission and back-scattering schemes incorporating a 25.4 mm detection window. The intensity ratios between the container and urea peaks in the collected spectra were different depending on the adopted measurement scheme. The intensity ratio was greatest (smallest container peak) in the NW-APO measurement due to the narrowed detection window, making the generated container Raman photons at the side-wall less detectable to the bottom-positioned detector. A spectral acquisition scheme allowing the maximal suppression of the container peaks, while still maintaining the sample features, was a key requirement to secure an accurate measurement of the sample concentration. In addition, a Monte Carlo simulation was used to visualize the distributions of the container and urea photons inside the sample-housed container.

Raman spectroscopy-in situ characterization of reversibly intercalated oxygen vacancies in α-MoO3

This work reports on the in situ strategy to reversibly generate or suppress oxygen vacancies on α-MoO₃ which were probed by Raman spectroscopy. Reversible changes in two features of the α-MoO₃ Raman spectrum could be correlated to the generation of oxygen vacancies: displacement of the T_b band frequency and the intensity decrease of the symmetrical stretching (ν_s) band. These two features could be used to qualitatively describe oxygen vacancies. Raman results also indicate that oxygen vacancies are located in the interlayer region of the α-MoO₃ lattice. This observation is corroborated by in situ X-ray diffraction, which also indicates the absence of nonstoichiometric phase transitions.

This work reports on the in situ strategy to reversibly generate or suppress oxygen vacancies on α-MoO₃ which were probed by Raman spectroscopy.

Poloxamer modified florfenicol instant microparticles for improved oral bioavailability

Surfactants can improve the hydrophobicity of poorly water-soluble drugs and increase the stability of microparticles by reducing surface tension. This study describes that surfactant-engineered florfenicol instant microparticles (FIMs) increase bioavailability through a micellar solubilization mechanism. The FIMs were prepared by a modified emulsification method, and the optimal prescription was obtained by a combination of single factor investigation and response surface methodology. The microparticles prepared in this study reduce the polymer materials while increasing the drug content. FIM has a smaller particle size and modification of poloxamer, resulting in better solubility and higher bioavailability. The in vitro solubility of FIM is 1.43 times higher than that of the bulk drug, and the dissolution equilibrium can be achieved in 10 minutes. Compared with florfenicol, FIM showed a decrease in T_max in the plasma concentration curve, with a peak concentration of 1.43 times and an area of 1.41 times. Considering the advantages of in vitro/in vivo performance and ease of preparation, FIMs may have great application prospects in pharmacy research.